Lifting mechanisms

ABSTRACT

A LIFTING MECHANISM INCORPORATING A POSITIVE BRAKE MEANS TO PREVENT UNCONTROLLED DESCENT OF THE LOAD WHEN THE LIFTING DRIVE IS DISCONTINUED. THE MECHANISM INCLUDES A GEAR WHEEL CONNECTED TO A ROTARY DRIVE MEANS AND MESHING WITH A SECOND GEAR WHEEL CONNECTED TO A ROTARY HOIST MEMBER, AND A LOCKING MEMBER ROTATABLY MOUNTED COAXIALLY WITH THE FIRST MENTIONED GEAR WHEEL AND HAVING A SPRAGGING GEAR PERMANENTLY IN MESH WITH THE FIRST MENTIONED GEAR WHEEL AND MOVABLE WITH THE ROTARY MOVEMENT OF THE FIRST MENTIONED GEAR WEEL BETWEEN A LOCKING POSITION WHEN THE SPRAGGING GEAR IS IN MESH WITH THE SECOND GEAR WHEEL AND A FURTHER POSITION IN WHICH THE SPRAGGING GEAR IS OUT OF MESH WITH THE SECOND GEAR WHEEL, MOVEMENT BETWEEN THE FIRST AND SECOND POSITIONS TAKING PLACE WHEN THE HOIST IS CAUSED TO RISE AND MOVEMENT IN THE REVERSE DIRECTION TAKING PLACE WHEN THE HOISE COMMENCES TO LOWER. CATCH WHEELS ARE PROVIDED TO MAINTAIN THE LOCKING MEMBER IN ITS SECOND POSITION TO ALLOW UNCONTROLLED LOWERING OF THE HOIST THROUGH THE ROTARY DRIVE MEANS. THE DRIVE MEANS MAY BE HAND OPERATED.

March 2, 1971 J. E. METCALF LIFTING MECHANISMS 5 Sheets-Sheet 1 Filed April 28, 1969 JOHN EDWARD METCALF,

lnvenlor BYIML'AMI Afforney H March 2, .1971 J. E. METCALF 3,566,709

. LIFTING MECHANISMS Filed April 28, 1969 5 Sheets-Sheet I JOHN EDWARD METCALF,

I nvenlor By, l FM Attorney 5 MarchZ, 1971 J. E. METCALF 3,566,709

LIF'IING MECHANISMS Filed A ril 28, 1969 5 Sheets-Sheet s JOHN EDWA RD METCALF Inventor By, UAZWZZ (xi Allorneys March ,2, 1971 J. E. METCALF 3,566,709

' mmme mzcnamsus Filed April 28, 1969 5 Sheets-Sheet I.

JOHN EDWARD METCALF,

I nventor rllduwfimil, 4 1 M, Attorney 5 March ,1 J. E. METCALF I 3,566,709

LIFTING MECHANISMS Filed A ril 28, 1969 s Sheets-Sheet 5 JQHN EDWARD METCALF,

lnvenlor y/ A pmb, Attorney 3 United States Patent 3,566,709 LIFTING MECHANISMS John Edward Metcalf, 63a Victoria St., Windsor, Berkshire, England Filed Apr. 28, 1969, Ser. No. 819,800 Int. Cl. B66d 1/76; F16d 41/24; F16h 57/10 US. Cl. 74-4115 9 Claims ABSTRACT OF THE DISCLOSURE A lifting mechanism incorporating a positive brake means to prevent uncontrolled descent of the load when the lifting drive is discontinued. The mechanism includes a gear wheel connected to a rotary drive means and meshing with a second gear wheel connected to a rotary hoist member, and a locking member rotatably mounted coaxially with the first mentioned gear wheel and having a spragging gear permanently in mesh with the first mentioned gear wheel and movable with the rotary movement of the first mentioned gear wheel between a locking position when the spragging gear is in mesh with the second gear wheel and a further position in which the spragging gear is out of mesh with the second gear wheel, movement between the first and second positions taking place when the hoist is caused to rise and movement in the reverse direction taking place when the hoise commences to lower. Catch wheels are provided to maintain the locking member in its second position to allow uncontrolled lowering of the hoist through the rotary drive means. The drive means may be hand operated.

This invention relates to lifting mechanisms primarily, but not necessarily exclusively, for light loads, for example of the order of one ton or less.

The object of the invention is to provide a lifting mechanism incorporating a positive brake means to prevent uncontrolled descent of the load when the lifting drive is discontinued.

A lifting mechanism in accordance with the invention comprises a gear wheel connected to a rotary drive means, a second gear wheel connected to a rotary hoist member and in mesh with the first-mentioned gear wheel, a locking member rotatably mounted co-axially with the firstmentioned gear wheel and having a spragging gear permanently in mesh with the first-mentioned gear wheel and movable with the rotary movement of the first-mentioned gear wheel between a position when the spragging gear is in mesh with the second gear wheel and a position in which the spragging gear is out of mesh with the second gear wheel, movement from the first to the second position being effected when the first-mentioned gear wheel rotates in a direction to cause the hoist to rise and movement in the reverse direction being effected when the first-mentioned gear wheel rotates in a direction to allow the hoist to be lowered.

In a preferred construction of the mechanism for manual operation, the first-mentioned gear wheel is fixed to a shaft rotatable by a winding handle and the rotary hoist member is a sprocket which engages a roller chain for lifting the load. The spragging gear is mounted on a plate freely rotatable about the first-mentioned gear wheel shaft and held in frictional contact therewith by a compression spring. A catch is provided to stop rotation of the plate to engage the spragging gear with both the meshing gear wheels when it is required to lower the hoist.

A preferred embodiment of the invention by way of example will now be described with reference to the accompanying drawings in which:

FIG. 1 shows a hoist according to the invention in section on the line I--I in FIG. 4;

ICC

FIG. 2 shows a further sectional view of the hoist on the line IIII in FIG. 1 with the hoist parts in a braked position;

FIG. 3 shows a view similar to FIG. 2 with the hoist parts in a winding position;

FIG. 4 shows a plan view of the hoist partly cut away with the hoist parts in a braked position; and

FIG. 5 shows a similar view to FIG. 4 with the hoist parts in a lowering or unwinding position;

As shown in the drawings the hoist is mounted on a framework 20, only part of which, consisting of the two parallel plates, is shown. A shaft 21 journalled in the frame work carries a gear wheel 2 between the plates and a winding handle 1 at one of its ends. A second shaft 22 also journalled in the framework and parallel with the first shaft 21 carries a gear wheel 5 which is in mesh with the gear wheel 2. Also fixed to the shaft 22 is a sprocket wheel 7 over which passes a length of roller chain 8, one end of which is attached to an anchorage 9 forming part of a platform or other support for a load to be hoisted. By manual rotation of the winding handle 1 in one direction or the other the roller chain is caused to move by the rotation of the sprockets so as to life or lower the hoist platform.

A rectangular locking plate 3- is freely mounted on the shaft '21 and carries a rotatable spragging gear 6 which is permanently in mesh with the gear wheel 2. The plate is forced into contact with an end surface of the gear wheel 2 by a coiled compression spring 4 loosely mounted on the shaft 21 and axially located by an abutment plate 26 secured to the shaft by a pin 27. As a result of the frictional force between the plate 3 and the gear wheel 2, rotation of the gear wheel to raise the load as shown in FIG. 3 causes the plate to rotate until it contacts a stop 23a forming part of a covering shell 23 attached to the framework 20 after which slipping occurs between the abutting faces of the plate and the gear wheel. When the winding handle is released after the load is raised to the required height as shown in FIG. 2, the load suspended by the chain initiates a reverse motion of the gear wheel 2 which carries the plate with it away from the stop 23a until the teeth of the spragging gear 6 comes into meshing contact with the teeth of the gear wheel 5. The consequent intermeshing of all three wheels, 2, 5 and 6 locks them together preventing further rotation and consequent lowering of the load attached to the anchor 9'.

In order that the load may be lowered the winding handle is first turned to commence raising the load once more so as to rotate the plate 3 towards the stop 13 and disengage the spragging gear from the gear wheel 5. By operation of the catch which will now be described, the plate is held in the position shown in FIGS. 3 and 5 so that the winding handle and gear train can be freely rotated to allow the load to be lowered.

The catch comprises a bar 25 freely slidably mounted in the framework parallel to the shaft 21. A coiled compression spring 10 is loosely mounted on the bar between one of the plates of the framework and a collar 11 fixed to the bar. The length of the spring 10 is such that in its uncompressed state the collar is clear of the plate 3 as shown in FIG. 4. The end of the bar remote from the spring 10 projecting through the framework abuts one end of the lever 12 which is loosely pivotally attached to the framework at its other end and lies between the winding handle and the framework. The winding handle is secured to the shaft 21 by a pivot pin 24 and carries a freely rotatable roller 13 which engages the exposed surface of the lever 12. The boss of the winding handle shaft is provided with a flat 28 to hold the handle in its position relative to the shaft 21 shown in FIG. 4 when the catch is inoperative for the hoist to be operated to raise 3 a load and prevent lowering. When the winding handle is pushed inwardly towards the framework as shown in FIG. 5, the lever 12 is also moved inwardly by its contact with the roller 13 and in turn moves the bar 25 axially to bring the collar 11 into line with the plate 3. When in this position the collar prevents the plate rotating to bring the spragging gear 6 into mesh with the gear wheel so that the load can be lowered while the winding handle is maintained in the position shown in FIG. 5. It will be clear that the catch affords a safety factor insofar that should an operator inadvertently release the handle while the load is being lowered the parts return to the position shown in FIG. 4 under the influence of the spring thus freeing the plate 3 which immediately rotates to mesh the spragging gear with the gear wheel 5 and lock the hoist against uncontrolled lowering.

The hoist mechanism described above is particularly useful for light loads which can be lifted by manual rotation through the winding handle 1 and can be mounted on a light hand truck carrying a framework supporting the hoist, the chain anchorage 9 being attached to a lifting platform of the truck. It should further be understood that the mechanism is not limited to such an application. For example, the winding handle can be replaced by a power drive from an electric motor, for example, to enable loads greater than those manually liftable to be dealt with. Moreover, the supporting framework for the mechanism can be fixed and attached to the structure of a workshop building.

What I claim is:

1. A lifting mechanism comprising a gear wheel connected to a rotary drive means, a second gear wheel connected to a rotary hoist member and in mesh with the first-mentioned gear wheel, a locking member rotatably mounted co-axially with the first-mentioned gear wheel and having a spragging gear permanently in mesh with the first-mentioned gear wheel and movable with the rotary movement of the first-mentioned gear wheel between a position when the spragging gear is in mesh with the second gear wheel and a position in which the spragging gear is out of mesh with the second gear wheel, movement from the first to the second position being effected when the first-mentioned gear wheel rotates in a direction to cause the hoist to rise and movement in the reverse direction being effected when the first-mentioned gear wheel rotates in a direction to allow the hoist to be lowered.

2. A lifting mechanism according to claim 1, wherein 4 the locking member comprises a plate freely rotatably mounted on a shaft carrying the first-mentioned gear wheel and supported in frictional contact with the firstmentioned gear wheel for movement therewith between the two positions during initial rotation of the first-mentioned gear wheel in one direction or the other.

3. A lifting mechanism according to claim 1, wherein the locking member is located in the second position by engagement with a fixed stop.

4. A lifting mechanism according to claim 1 including a releasable catch to prevent movement of the locking member into the first position to allow free rotation of the first-mentioned gear wheel to allow the hoist to be lowered.

5. A lifting mechanism according to claim 4, wherein the catch comprises a collar mounted on a slidable rod for movement into abutting relationship with the locking member to prevent movement thereof into the first position.

6. A lifting mechanism according to claim 5, wherein .the collar is held out of engagement with the locking member by a coiled compression spring mounted on the rod bet-ween the collar and the fixed abutment.

7. A lifting mechanism according to claim 6 in which the rod is movable to bring the collar into engagement position with the locking member by means connected to the rotary drive means.

8. A lifting mechanism according to claim 7, wherein said means comprises a lever engaging an end of the rod in abutting relation with a winding handle pivotally mounted on the shaft of the first-mentioned gear wheel and forming the rotary drive means therefor.

9. A lifting mechanism according to claim 1 wherein the rotary hoist member comprises a sprocket secured to a shaft carrying the second-mentioned chain connectable to a load to be lifted by the lifting mechanism.

References Cited UNITED STATES PATENTS 9/1959 Alwood 254X 1/1963 Glaze l92-4X LEONARD H. GERIN, Primary Examiner 

